The present invention relates to a vibration table and, more particularly, to a vibration table that provides substantially uniform vibration across the table to test a plurality of devices mounted on the table for device reliability.
Shaker or vibration tables are often used in an assembly line to screen devices for any possible defects which may result or may have resulted from the manufacturing process. In this manner, products which have defects identified by the vibration table may be screened out of the production line process before being shipped to a customer. Often vibration tables are used in conjunction with a heating and cooling temperature cycling or burn in chamber so that the devices can be further screened for defects that may arise from exposure to elevated and lowered temperatures or from the combined synergism of both temperature and vibration.
Typical vibration tables include a base and a floating platform on which devices are secured or mounted for testing. The vibration table includes a plurality of vibration assemblies or "hammers", which are secured to the lower surface of the platform to induce vibration in the platform. The vibration assemblies are typically secured to the platform at angles between thirty five degrees (35.degree.) to forty-five degrees (45.degree.) with respect to the vertical axis to induce vibration pulses in three axes of the platform. FIGS. 21 and 22 illustrate a standard vibrator to table mounting configuration for pneumatic vibrator vibration systems, i.e., a horizontal table with vibrators attached to the horizontal plane. There are varying modifications made to this arrangement by different table manufactures in an effort to produce more desirable table acceleration characteristics, i.e. consistent acceleration levels from point to point and in all three axes (x, y, and z). For example, the vibration tables described in U.S. Pat. Nos. 4,181,026; 4,181,027; 4,181,208; and 4,181,029 each use multiple layers of honeycomb and elastomers to spread and dampen the localized vibration energy of each vibrator. U.S. Pat. Nos. 5,412,991; 5,589,637; 5,675,098; 5,744,724; and 5,836,202 disclose vibration tables which incorporate a very thick aluminum plate for rigidity with cored-out sections to reduce the weight. In U.S. Pat. No. 5,594,177, a table is disclosed which uses two thin aluminum plates separated by spaces to achieve rigidity while still reducing the table weight.
Vibration tables available from THERMOTRON include spacers mounted on top of the table for product mounting to try and isolate the product from acceleration hot spots. As illustrated in FIGS. 21 and 22 with these standard mounting techniques, there are only three primary force vectors, i.e. a, b, and c. Depending on the rotational position of the mounted vibrator, forces a and b may be imparting acceleration forces in an x direction, a y direction or any angle between the two. Although the plate is solid in most cases, and vibration energy will be distributed over the entire plate, the energy imparted by the vibrator will be greater directly over the vibrator than any other place on the plate.
Notwithstanding these various improvements, heretofore, known vibration tables do not achieve uniform vibration across the platform. As a result, one part on the platform is subjected to one set of vibration levels and another part in another section of the platform is subjected to another set of vibration levels. Consequently, multiple parts tested by a presently known vibration table may not be tested or screened at the same stress levels.
Accordingly, there is a need for a vibration table that can generate substantially uniform vibration energy across the full spectrum of the platform support surface along each of the axes in order to provide a reliable testing procedure.